Toolholder

ABSTRACT

The invention relates to a toolholder for holding a tool at one end and having a tubular shank at its other end for mounting it into the bore of a support member. The shank has at least two circumferentially spaced perforations in its tubular wall. Each of the perforations extends obliquely toward the front of the shank as it extends from the inner to the outer surface of the tubular wall. 
     A locking element is located partially within each of said perforations and the recess formed by the inner surface of the tubular shank. An actuating mechanism is located within the recess to drive the locking elements outwardly against the walls, thereby expanding the rear of the tubular shank to lock the shank in the support member bore.

BACKGROUND OF THE INVENTION

This invention relates to toolholders. It is especially concerned with abody having at least one cutting insert seat on one end and a shankreceivable in the bore of a tool support member on the other end. Suchtools are used in the cutting and shaping of workpieces where it isimportant that the toolholder be held in a rigid manner so that bothmovement and vibration are minimized during the metalcutting operation.

Many devices in the prior art have proven to be successful in thisregard and are exemplified by McCreery U.S. Pat. Nos. 3,498,653; McCrayet al 4,135,418; Heaton et al 4,197,771; and Friedline 4,350,463. Theforegoing devices are concerned with the use of ball-like lockingelements to hold the shank of a toolholder in the bore of the toolsupport member.

One drawback common to the foregoing designs is the feature that thelocking elements in each must abut against at least one surface duringlocking that is not similar in size and shape to the locking elementabutment surface. This produces small contact areas with high contactstresses leading to plastic deformation of the locking elements and thesurfaces they abut against each time the toolholder is locked onto asupport member. After many repeated uses, the deformation in the lockingelements and the surfaces they abut against can lead to a reduction inthe rigidity of the toolholder, thus shortening its useful lifetime.

There is, therefore, clearly a need for a toolholder and a toolholderassembly design which has a longer lifetime. This design must, however,be capable of being easily and accurately manufactured. It should alsobe capable of being compactly sized so that it can be used in a widerange of applications, including small diameter boring bars.

SUMMARY OF THE INVENTION

I have surprisingly found that the present invention addresses theforegoing needs in that a toolholder is now provided that has a longlifetime, and yet can be made compactly and is also both easily andaccurately manufactured.

In the present invention, a toolholder shank for mounting in a borethrough a forwardly facing surface of a tool support member is provided.The shank has a tubular portion which is perforated by perforations atat least two circumferentially spaced locations. Each of theseperforations contains a forwardly facing concave abutment surface whichextends forwardly while extending from the inner surface toward theouter surface of the tubular shank.

In a preferred embodiment, the shank is an integral part of a toolholderhaving a forward end for receiving a tool. The toolholder also has arearwardly facing abutment face for abutment with the tool supportmember surface that contains the bore in which the toolholder shank willbe received. In addition, a key or keyway is present on the toolholderfor holding the tool nonrotatable with respect to the tool supportmember. Furthermore, a section of the tubular shank portion locatedrearwardly of the forwardly facing concave abutment surfaces isresiliently expansible for abutment with the support member bore.

Preferably, the forward facing abutment surfaces in the perforations areconcave, and more preferably, are concave cylindrical surfaces. Mostpreferably, these abutment surfaces have a radius of curvature which isat least equal to, but no greater than, about 0.004 inches, and morepreferably about 0.002 inches, larger than the radius of curvature ofthe convex spherical abutment surfaces of the locking elements whichwill abut against these toolholder surfaces.

Preferably, the outer surface of the tubular shank portion tapersinwardly as it extends rearwardly, and more preferably, the outersurface is a frustoconical surface.

Preferably, the mechanism for holding the toolholder nonrotatable is oneor more slots or keyways in the rear of the tubular shank which aredesigned to receive one or more keys in the bore of the tool supportmember.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects of the present invention will becomemore apparent upon review of the following detailed description of theinvention in conjunction with the drawings which are briefly describedbelow:

FIG. 1 shows a perspective view of an embodiment of a toolholder inaccordance with the present invention.

FIG. 2 shows a side plan view of an embodiment of a toolholder assemblyin accordance with the present invention in partial cross section.

FIG. 3 shows a longitudinal cross section along a diameter of thetoolholder shank shown in FIG. 1.

FIG. 4 shows a perspective exploded view in partial cross section of theembodiment of the toolholder lock up mechanism and a toolholder supportmember shown in FIG. 2.

FIG. 5 shows a diametric longitudinal cross section of the forward endof the lock up bar in accordance with the present invention as shown inFIG. 4 viewed along V--V.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, FIG. 1 shows an embodiment ofa toolholder 10 having a forward end 12 and a rearward tubular shank 16attached to the forward end 12. On the forward end 12 is a pocket 14 forreceiving a cutting tool. The pocket 14 is conventional in design and isdesigned to receive an indexable cutting insert, locking pin and shim(not shown). It should be understood, however, that the presentinvention is not limited to the forward end design shown in FIG. 1, butincludes by way of example and not limitation forward ends havingmultiple insert seats such as may be found on a milling cutter. Inaddition, the forward end may be a non-cutting tool.

At the juncture of the forward end 12 and the shank 16 is a rearwardlyfacing abutment face 15 for abutment with the forwardly facing surfaceof a tool support member. Preferably, face 15 is planar and is orientedat 90 degrees to the longitudinal center line X--X of shank 16.

As shown in FIG. 1, the tubular shank 16 is preferably an integral partof the toolholder 10, and is preferably machined from a single piece ofsteel. However, it is also contemplated that the tubular shank 16 andthe forward end 12 of the toolholder may be independent pieces that maybe subsequently mechanically joined together with the rearwardly facingabutment face 15 being a part of either the forward end 12 or the shank16. In this manner, a single shank may be utilized with a variety ofdifferent toolholders or other tool components.

The shank design of the present invention may also be used in segments,extensions or assembly components of a modular boring system. In fact,it is envisioned that the present shank design may be used in aplurality of segments to join one segment to the next.

As shown in FIG. 1, the tubular shank 16 has a frustoconical shape andis perforated at two circumferentially spaced locations by perforations18, the walls 20 of which communicate with shank inner surface 22 andouter surface 24. While preferably, as shown in FIG. 1, the tubularshank has two perforations 18 circumferentially spaced at 180 degrees toeach other, it may be desired in large shank diameters that there bethree or four circumferentially spaced perforations 18.

Circumferentially spaced between perforations 18 are slots 26 and 28 onthe end of the tubular shank 16. These slots 26 and 28 are designed toserve as keyways to accept keys in the tool support member bore andthereby hold the toolholder nonrotatable with respect to the toolsupport member. In addition, by locating the slots at the rear end ofthe tubular shank, the flexibility of the portion of the shank behindthe perforations can be readily controlled by changes in the location,size and number of slots. In the embodiment shown in FIG. 1, only slot26 located in line with the cutting tool receiving pocket 14 is utilizedas a keyway to hold the toolholder nonrotatably insofar as the width, w,of slot 26 is dimensioned to provide a slip fit with a key whereas thewidth of slot 28 is slightly larger (e.g., 0.010 inches greater) thanthe width of slot 26. This provides the added benefit that the tubularshank can be readily received in a tool support bore provided with twokeys in order to accept both right handed and left handed toolholders(i.e., cutting tool pocket on the left or right hand side of thetoolholder).

In an alternative embodiment (not shown) the location of theperforations 18 and slots 26 and 28 may be rotated ninety degrees fromthat shown in FIG. 1 about the longitudinal axis X--X of the shank sothat one of the perforations 18 is aligned with the cutting toolreceiving pocket 14.

In accordance with the present invention, the toolholder 10 is mountedon a tool support member 30 via locking elements 32. As shown in FIG.2., these locking elements 32 preferably are two spherical balls (i.e.,spheres) which are held partially within the perforations 18 by alocking rod 34 nonrotatably contained within a longitudinal passageway36 in stub 38. The locking rod 34 has two cylindrical shaped ramps 40which drive the balls 32 outwardly through radial apertures 42 in stub38 when the locking rod 34 is pulled rearwardly as shown in FIG. 2.

As the locking balls are moved outwardly by ramps 40, they are driveninto abutment with the forwardly facing abutment surfaces 44 inperforations 18 and rearwardly facing concave surfaces 46 in the radialapertures 42 of the stub 38. In this manner, a rearwardly force isdirected against the toolholder 10 such that the rearwardly facingabutment shoulder 15 on the toolholder 10 is placed in pressurizedabutment with the forward facing surface 50 of the tool support member30.

At the same time that this is occurring, the locking elements 32 inaddition to exerting a rearwardly directed force also exert an outwardlydirected force against the forwardly facing abutment surfaces 44 inapertures 18 and thereby resiliently expand the sections 52 of the shankouter surface 24, located rearwardly of abutment surfaces 44, intoabutment with the bore 48 of the tool support member 30.

Also shown in FIG. 2 is the engagement between key member 54 and slot 26which act to hold the toolholder 10 nonrotatable with respect to thetool support member. These members are circumferentially located at 90degrees to perforations 18.

These various components of the toolholder assembly, in accordance withthe present invention, are shown more clearly in the remaining figures.

In FIG. 3, which is a cross section taken through the tubular shank 16along a plane containing a shank diameter and the center lines P--P ofperforations 18, it is clearly shown that perforations 18 preferablyform walls 20 that are cylindrical in shape and have a radius ofcurvature r_(c). These perforations 18 are angled with respect to thelongitudinal center line X--X of the shank at an angle B such that therotational axis of symmetry P--P, and more importantly, forwardly facingconcave abutment surfaces 44 on walls 20 extend forwardly whileextending away from the inner surface 22 toward the outer surface 24 ofthe tubular shank 16. While it would be preferred that angle B is aslarge as possible to maximize mechanical advantage, at large angles,machining tolerances may interfere with the proper locating of thelocking elements 32 against surfaces 44. It is, therefore, preferredthat angle B is 50 to 60 degrees.

Concave forwardly facing abutment surfaces 44 have a radius of curvaturer_(c), the value of which is determined by the radius of curvature,r_(s), of the concave abutment surface of the locking elements 32 whichwill abut against surfaces 44 (see FIG. 2). It is preferred that r_(c)and r_(s) be as close as possible to each other so that, when thelocking elements 32 are abutted against surfaces 44, contact occurs overas large an area as possible in order to minimize deformation to thesurface 44 and to the locking element surface, thereby prolonging theiruseful lifetimes. Preferably, in order to achieve this result, it ispreferred that r_(c) is equal to, but no greater than, 0.004 inches, andmore preferably 0.002 inches,larger than r_(s).

It is important that the abutment surfaces 44 have the radius and slopedescribed. It is also important that abutment surfaces 44 be at the sameheight in a direction parallel to the X--X axis to assure lockup occursin both abutment surfaces. However, the other portions of theperforation walls 20 that are not used for abutment with the lockingelements may deviate from the above described relationships withoutaffecting the performance of the present invention. Nonetheless, fromthe point of view of manufacturing ease, it is preferred that the entiresurface of perforation walls 20 have the r_(c) and B described above inthat the perforations 18 may be simply and accurately made by drillingholes with a twist drill or by milling with an end mill of the requireddiameter held at the appropriate angle at the same distance fromrearwardly facing abutment face 15.

The outer diameter of the tubular shank 16 decreases as the shankextends rearwardly. Preferably, this decrease is gradual and providesouter surface 24 with a frustoconical shape as shown in FIG. 1. Theangle, A, that surface 24 forms with the shank center line X--X, whilepreferably as small as possible in order to minimize shank diameter foruse with small diameter support members (e.g., small diameter boringbars), must be large enough to allow the shank to be easily loaded intothe bore 48 of the tool support member 30 which has an angle of taperslightly larger (e.g., 5 minutes of arc) than angle A as shown in FIG.2. I have found that setting angle A equal to four degrees adequatelyaddresses both concerns.

An internal cavity 56 is formed in tubular shank 16 by inner generallycylindrical surface 22 which is joined by rearwardly facing surface 58at the forward end of the tubular shank. The cavity 56 has been sized toloosely accept the lock up mechanism shown in FIG. 2. At its rearmostend, surface 22 is joined by a radially outwardly flaring surface 60which extends to the rear surface 61 which joins it and outer surface24. The outwardly flared surface 60 serves to ease loading of thetubular shank 16 over stub 38.

FIG. 4 shows an exploded view of the components shown in FIG. 2, withthe toolholder 10 and locking pins 32 removed for clarity. The toolsupport member 30 is shown having forwardly facing abutment surface 50perforated by bore 48. The bore surface 62 in the forwardmost sectiontapers inwardly toward the center line of the bore 48 at an angle whichis slightly larger than angle A on the tubular shank 16 as it recedesfrom forward face 50 until it joins cylindrical bore surface 64. Thebore 48 is preferably perforated through its forward tapered surface 62by two diametrically opposed apertures 66 which hold cylindrical keys 54which are press fit in apertures 66 and which extend into bore 48. Thesupport member further contains holes 68 (only one of which is shown)for receiving bolts (not shown) for joining support member 30 to alarger machine tool (not shown), such as a lathe turret, spindle, boringbar, etc. It should be further understood that support member 30 may bean integral part of, and not separate as shown, of such a turret,spindle, boring bar, etc.

The locking element actuating mechanism includes the lock rod 34 and thestub 38. The lock rod 34 has an abutment member 70 joined to anattachment member. Attachment member is shown here as externallythreaded rod 72. The abutment member 70 has an end surface 74 joined toan oppositely facing shoulder 76 by a side surface 78. Preferably, theend surface 74 may be used for abutment against surface 58 of thetoolholder 10 when the locking rod is pushed forward to unlock thetoolholder 10 from the tool support member 30. In this manner, lock rod34 and end surface 74 may be used to lift the toolholder 10 off thesupport member 30.

Side surface 78 is a cylindrical surface which has been intersected byradially outward facing concave surface depressions 80 which areequidistant from end surface 74 and circumferentially spaced at 180degrees to each other. These depressions 80 have been dimensioned toreceive locking elements 32 in the unlocked position. The depressions 80as shown are elongated in the direction of the longitudinal axis Y--Yand preferably have a concave spherical surface at each longitudinal endwith a radius r₁ that is equal to or slightly larger than the radius ofthe locking element 32. The radial depth of depressions 80 intocylindrical side surface 78 is set so that the sum of the thickness oflock rod material separating depressions 80 plus the two diameters ofthe locking elements 32 is less than the internal diameter of the shank.

As most clearly shown in FIG. 5, joining depressions 80 at the samelongitudinal end of each depression are ramps 40, one for eachdepression 80. Each ramp 40 declines inwardly toward central axis Y--Yas it extends away from end 74 until it joins depressions 80. Thesurface of ramp 40 is a concave cylindrical surface of revolution havinga radius r about an axis Z--Z tilted on an angle C to central axis Y--Y.Radius r is again equal to or slightly larger than the radius of thelocking element 32 and is preferably no greater than 0.004 inches, andmore preferably 0.002 inches, larger than r_(s).

While angle C should ideally be as small as possible to maximizemechanical advantage, this ideal configuration must be balanced againstthe ability to manufacture within a given tolerance and the concern thatthe shallower C is the longer the ramp becomes and the longer the lockrod must be. I have found that setting angle C equal to 20 degrees to bea preferred compromise between these competing concerns, with angle Cbeing equal to 15 degrees being more preferred.

The radial depth into the lock rod at which the ramps 40 intersectdepressions 80 is deep enough to assure that the lockup always takesplace on ramps 40 and not at the intersection of the ramps 40 and thedepressions 80 or within depressions 80. However, the maximum value thatthe aforementioned radial depth may be designed to have is preferablylimited to reduce the length of travel of the lock rod required toachieve lockup

As shown in FIGS. 2 and 4, the diameter of lock rod 34 has beendimensioned to loosely engage in longitudinal passageway 36communicating between the front surface 82 and the rear surface 84 ofstub 38. When engaged in passageway 36, lock rod 34 is heldnon-rotatable by the engagement of keyway 86 and key 88 which extendsinto passageway 36. Key 88 may be a set screw 90 threadedly engaged witha threaded radial aperture 92 in stub 38.

When engaged in the stub 38, the lock rod is reciprocally movableforwardly and rearwardly and is held captive between forward facingannular shoulder 94 and key 88. It should be understood, however, thatin alternative embodiments the means by which the lock rod 34 is heldnonrotatable and captive within the stub 38 may be by members externalto the lock rod 34 and/or stub 38.

When fully engaged in the stub 38, the threaded rod 72 of the lock rod34 is engaged with another member (not shown) which will act toreciprocate the lock rod forwardly, for unlocking, and rearwardly, forlocking. In addition, when fully engaged in stub 38, the diametricallyopposed depressions 80 will align with diametrically opposed radialapertures 42 which communicate between the side surface 96 of stub 38and passageway 36, when the lock rod 34 is in the unlocked position. Inthe locked position, ramps 40 will align with apertures 42 as shown inFIG. 2.

An annular groove 98 is formed in side surface 96 in a location on thestub 38 such that it intersects the rearward end of apertures 42.Contained in the groove 98 is an elastomeric O ring 100 which is used toretain the locking elements 32 within apertures 42 when in the unlockedposition.

Flange 102 of the stub 38 is pierced by longitudinal holes (not shown)for accepting bolts (not shown) for mounting the stub 38 on the toolsupport member 30.

The combination of locking elements 32, locking rod 34 and stub 38 formsthe locking mechanism, and this mechanism is then joined to a toolsupport member 30 via bolts which are not shown. The locking mechanismsits within a tapered bore of the tool support member. The tapered borepreferably contains two keys 54 which are located at 180 degrees to eachother and at 90 degrees to the locking elements 32. Keys 54 fit withinthe slots 24 and 26 on the end of the tubular shank 16.

Additional preferred embodiments of shanks, toolholders and othertoolholder components are described in my copending application Ser.Nos. 007,070; 007,169; 007,309; and 007,310 filed concurrently with thepresent application.

All patents and patent applications previously referred to in thisapplication are hereby incorporated by reference.

Changes and modifications in the specifically described embodiments canbe carried out without departing from the scope of the invention whichis intended to be limited only by the scope of the appended claims.

What is claimed is:
 1. A toolholder for mounting in a bore in aforwardly facing surface of a tool support member, said toolholdercomprising:a forward end having a tool receiving means thereon; arearwardly facing abutment face for abutment with the forwardly facingsurface of the tool support member; a tubular shank portion open at oneend, connected to said forward end, and extending rearwardly away fromsaid forward end; said tubular shank portion perforated by perforationsat two circumferentially spaced locations; a forwardly facing concaveabutment surface in each of said perforations; said forwardly facingconcave abutment surface extending forwardly while extending away fromthe inner surface of said tubular shank toward the outer surface of saidtubular shank; and means for holding said toolholder nonrotatable withrespect to said tool support member.
 2. The toolholder according toclaim 1 wherein said tubular shank portion has an outer diameter whichdecreases as the shank portion extends rearwardly.
 3. The toolholderaccording to claim 1 wherein the outer surface of the shank portionforms a frustoconical shape with the smallest diameter rearmost.
 4. Thetoolholder according to claim 1 wherein said perforations when viewedalong the axis of symmetry of each perforation have cross sections whichare circular.
 5. The toolholder according to claim 1 wherein the axis ofrevolution of said concave abutment surface is inclined to the axis ofrevolution of said tubular shank at an angle between 50 and 60 degrees.6. The toolholder according to claim 1 wherein said means for holdingsaid toolholder nonrotatable is located on said tubular shank portion.7. The toolholder according to claim 6 wherein said means for holdingsaid toolholder nonrotatable is circumferentially spaced between saidperforations.
 8. The toolholder according to claim 1 wherein said twocircumferentially spaced locations are at 180 degrees to each other. 9.A toolholder for mounting in a bore through a forwardly facing surfaceof a tool support member, said toolholder comprising:a tubular shankportion receivable in said bore; the wall of said tubular shank portionperforated by a first and a second perforation at two circumferentiallyspaced locations; a first forwardly facing concave abutment surface insaid first perforation; a second forwardly facing concave abutmentsurface in said second perforation; and said first and second forwardlyfacing abutment surfaces extending forwardly while extending away fromthe inner surface of said tubular shank portion.
 10. The toolholderaccording to claim 9 further comprising:a means for holding saidtoolholder nonrotatable with respect to said tool support member. 11.The toolholder according to claim 9 further comprising:a rearwardlyfacing abutment face for abutment with the forwardly facing surface ofsaid tool support member.
 12. The toolholder according to claim 9further comprising:a tool receiving means connected to said tubularshank portion.
 13. The toolholder according to claim 11 furthercomprising:a means for holding said toolholder nonrotatable with respectto said tool support member.
 14. The toolholder according to claim 12further comprising:a means for holding said toolholder nonrotatable withrespect to said tool support member.
 15. The toolholder according toclaim 12 further comprising:a rearwardly facing abutment face forabutment with the forwardly facing surface of said tool support member.16. The toolholder according to claim 14 further comprising:a rearwardlyfacing abutment face for abutment with the forwardly facing surface ofsaid tool support member.
 17. The toolholder according to claim 9wherein said first perforation is located at 180 degrees to said secondperforation.
 18. A toolholder for mounting in a bore through a forwardlyfacing surface of a tool support member, said toolholder comprising:aforward end having a tool receiving means thereon; a rearwardly facingabutment face for abutment with the forwardly facing surface of the toolsupport member; a tubular shank portion connected to said forward endand extending rearwardly away from said forward end; said tubular shankportion perforated by a first perforation and a second perforation at180 degrees to said first perforation; a first forwardly facingcylindrical concave abutment surface in said first perforation; a secondforwardly facing cylindrical concave abutment surface in said secondperforation; said first and second concave abutment surfaces extendingforwardly while extending away from the inner surface of said tubularshank portion; the outer diameter of said tubular shank portiondecreasing as said tubular shank portion extends rearwardly; and a meansfor holding said toolholder nonrotatable with respect to said toolsupport member, said means for holding nonrotatable located on saidtubular shank circumferentially between said first and said secondperforations.
 19. The toolholder according to claim 18 wherein saidfirst and said second concave cylindrical abutment surfaces are inclinedat an angle between 50 and 60 degrees from the center line of saidtubular shank portion.
 20. The toolholder according to claim 18 whereinthe walls of said first and second perforations are completelycylindrical.
 21. The toolholder according to claim 1 wherein a sectionof said tubular shank portion located rearwardly of said forwardlyfacing concave abutment surfaces is resiliently expansible for abutmentwith said bore.
 22. The toolholder according to claim 9 wherein asection of said tubular shank portion located rearwardly of said firstand second forwardly facing concave abutment surfaces is resilientlyexpansible for abutment with said bore.
 23. The toolholder according toclaim 18 wherein a section of said tubular shank portion locatedrearwardly of said first and second forwardly facing cylindrical concaveabutment surfaces is resiliently expansible for abutment with said bore.